Optical Tweezer System

HARPENDEN, UK, Jan. 28, 2010 – Elliot Scientific Ltd. has introduced a new version of its E3500 computer-controlled multiple-trap optical tweezer system with E4100 quadrant photodetector (QPD) force measurement capability. The system uses two fiber-coupled lasers: one for trapping and the other for the probe beam. It comprises an optical module containing the laser, beam-steering optics, a microscope interface, a control module with drive electronics, a computer and control software. Also included are a computer monitor and a laser blocking filter. The tweezer was built into a high-end Nikon microscope.

Suitable for multiple spot trapping and manipulation of micron-size particles, the system is designed to be attached to high-quality commercial instruments, upgrading them to photonic force microscopes. Applications include cell sorting, microrheology, colloid research and particle spectroscopy.

Features of the optical tweezer system include independent control of multiple traps and arrays, manipulation via computer-controlled acousto-optic beam-steering optics or the microscope X-Y sample stage, a graphical user interface for mouse control of optical traps, Z-trapping using a microscope focus stage, and linear or circular trapping arrays with variable spacing and rotation. Also included are a high-speed camera and a 1070-nm fiber laser with variable power for changing the strength of the optical trap. The laser provides a TEM00 beam with M2 of 1.05. The high beam quality, when used with high-numerical-aperture microscope objectives provides the tightly focused Gaussian spot required for efficient optical traps in both X-Y and Z-directions. The system attaches to the camera or to an epifluorescence port.

Optical traps are created and positioned by mouse control in the software. They can be single spots, or linear or circular arrays. The spacing, orientation and number of traps can be adjusted from the software’s control panel. Additional traps can be added or removed at any time, without affecting existing ones, and multiple arrays and spots can be manipulated independently of each other anywhere within the field of view.

The high-speed camera with Gigabit Ethernet enables visualization of the trapped particles through the computer interface. The trap positions are overlaid on the video image to facilitate particle trapping.

QPD force measurement via the E4100 accessory can be added to any of the company’s optical tweezer systems. It enables the user to monitor the position of a trapped particle with nanometer accuracy. The measurement software lets the user calibrate the motion of a single trapped object and infer the forces exerted. Several configurations are available within the E4100 range. The company can supply a complete force measurement optical tweezer plug-and-play system, or the capability can be added to an existing tweezer installation. Retrofitting to a good-quality microscope is also an option, as are multiple QPDs and an auxiliary probe beam.

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